The present invention relates to a valve timing control apparatus of an internal combustion engine.
German Pat. No. DE 40 41 943 C2 describes a valve timing control apparatus for internal combustion engines, including a clutch unit for coupling a driving timing pulley with a driven camshaft. Two plungers, each surrounded by a spring, are operated by a swivel arm, coupled to the camshaft, for movement in axial direction. Each spring has one end which is connected to a hydraulically operated slide. Upon adjustment of the slides in a first displacement direction, one spring turns and detaches from the plunger whereas an adjustment in a second displacement direction effects a turning of the other spring and detachment thereof from the associated plunger. As a result of the detachment, the swivel arm can move relative to the timing pulley in one direction until a spring winding lies in a respective groove, so that the spring windings occupy a slanted disposition and prevent a further displacement of the plunger as a consequence of increased friction forces between spring and plunger.
German Pat. No. 40 34 406 C2 discloses a valve timing control apparatus which includes two devices between a driving chain wheel and a driven camshaft, with each device having a substantially smooth pair of boundary surfaces. Adjustment of the rotation angle between the camshaft and the chain wheel is realized by rolling a boundary surface of one of these smooth pairs of boundary surfaces through hydraulic means upon the respectively associated boundary surface until reaching a stop member, or the boundary surface of one of these smooth pairs of boundary surfaces is axially shifted at an angle of inclination with respect to the surface. The boundary surface of the second device, providing the adjustment in the opposite direction, is "pulled along".
British Pat. No. GB 2 248 098 A describes a valve control apparatus for internal combustion engines, including an axially movable hollow actuating element having a bore through which a spring-biased ball projects into a groove formed in a rotatable second element connected to the camshaft. The groove is arranged at an angle with respect to the direction of displacement of the actuating element, so that a displacement of the actuating element results in a rotation of the second element. The second element is coupled with a plurality of circumferential clamps, with rollers being disposed in circumferential direction between the clamps at a distance with is kept constant by the clamps. The rollers are guided externally upon an inner cylindrical surface, which is coupled with a driving timing pulley, and internally by surfaces which are arranged along the circumference of an element, coupled to the camshaft, at an inclination relative to the tangent of this circumference. The inclination of these surfaces is provided in opposite direction with respect to two neighboring circumferential rollers. Thus, a displacement of the actuating element in a first direction in opposition to the force of a spiral spring results in an adjustment of the rotation angle in one direction until the rollers, inclined in one direction, are wedged between the inclination and the inner cylindrical surface. A release of the actuating element realizes a relative rotation in opposite direction until the rollers associated to the respective inclination are wedged accordingly.
A further valve control apparatus is known from U.S. Pat. No. 5,235,941 which operates similar to the valve control apparatus described in British Pat. No. GB 2 248 098 and also uses a plurality of roller pairs, whereby a respective roller is so jammed in the end positions of the travel path toward the camshaft in radial direction, that the driving timing pulley and the driven camshaft are in fixed rotative engagement. No jamming of the rollers occurs in the area between these end positions, so that the rotational relation between the camshaft and the timing pulley can be adjusted.
Although a configuration of valve control apparatuses based on a jamming action of the rollers in the extreme end positions seems to be sound because the overall structure can be kept comparably small, their manufacture is not cost-efficient and pose the risk of an excessive jamming of the rollers in their end positions when, for example, the clamping areas become contaminated or corroded, or when excessive load moments are applied, so that an adjustment is no longer possible. Moreover, there is a risk that the rollers or of their running or clamping surfaces deform as a consequence of applied fairly high clamping loads over an extended time, so that the precision of the adjustment is adversely affected. Prevention and elimination of these defects, created during extended exposure to loads, require therefore exchangeability of respective, cost-intensive components.